Data is commonly transported through networks in packets, frames or cells; these terms e.g., packets, frames, cells, data streams, packet streams, frame streams and cell streams, are used interchangeably throughout this specification. In multicasting, copies of data from a single source are sent to multiple destinations over a network supporting the Internet protocol (IP for short). IP multicast uses a multicast group destination address which is shared by a group of hosts (end users). A multicast source sends packets to that address and when a multicast router or switch (commonly called as “routing device”) receives such a packet (addressed to the multicast address), it replicates and delivers the packet to multiple receiving hosts within an internet routed infrastructure. The multicast router compares the received multicast packets to a multicast forwarding table and sends a copy of the received packets out all the interfaces named in that multicast forwarding table. DSL access systems can be used to deliver multicast data streams from the routing device to a host or a group of hosts. A variety of DSL (xDSL) systems are available, e.g., HDSL (High bit rate DSL), SDSL (Symmetric DSL), RADSL (Rate Adaptive DSL), ADSL (Asymmetric DSL) and VDSL (Very high bit rate DSL).
Internet Group Management Protocol (IGMP) is the preferred signaling protocol used in IP networks supporting multicast communications. IGMP messages are separate from packets used for data transfer. Hosts and routing devices use IGMP messages to report their IP multicast group memberships to any neighboring multicast routing devices. For example, when the host joins or leaves the multicast group, the IGMP message indicating this fact is transmitted to the neighboring routing devices
Following U.S. patent documents describe related subject matters.
U.S. Pat. No. 6,654,371 Nov. 25, 2003 Dustan et al describes “Method and Apparatus for Forwarding Multicast Data by Relaying IGMP Group Membership”
U.S. patent application Ser. No. 2002/0097728 published Jul. 25, 2002 Hinderks et al describes “Method and Apparatus for Injection of IP Multicast Content into an ATM DSL Network”.
U.S. patent application Ser. No. 2002/0191631 published Dec. 19, 2002 Couty describes “Method of and a System for Lightening the Signaling Load of a Multicast Protocol applied to a Network of Terminals using a Transmission Medium that does not support Mutual Listening between Terminals”.
U.S. patent application Ser. No. 2003/0145102 published Jul. 31, 2003 Keller-Tuberg describes “Facilitating Improved Reliability of Internet Group Management Protocol through the Use of Acknowledge Messages”
Referring to FIG. 1, a source 30 is injecting a multicast data stream 32 to a network 34 which can be, for example, an ATM network or an IP network. Downstream, a DSL access system, such as a DSLAM 38 (Digital Subscriber Line Asynchronous Multiplexer) delivers the data stream 32 to multiple end users through DSLs 36. Each end user generally has a host computer or a set-top box 40 with a viewing device that is connected to a DSL by way of a CPE 42 (Customer Premise Equipment). In other cases, as shown in FIG. 1, one CPE 44 may interface between a DSL 46 and multiple of end users on a local area network (LAN) 48 of any type e.g., an ATM network, an Ethernet, etc. The CPE includes a DSL modem which bridges the customers system and the DSL.
Referring further to FIG. 1, the DSLAM 38 interfaces between network 34 and CPEs 42, 44. The DSLAM 38 includes an NT (Network Termination) 45 and one or more LTs (Line Termination) 47. The NT manages termination of a point-to-multipoint connection between DSLAM and CPEs. Each LT is essentially a DSL card which manages termination of DSL connections of data streams towards its CPE. A suitable transport medium, such as a bus, switching fabric or point-to-multipoint connections, for example, is provided between NT and LTs.
For the connection over the DSL link 36, ATM has been widely regarded as the communication protocol for use between a DSLAM to a DSL modem. The Alcatel 7300 ASAM (Advanced Services Access Manager) is an example of a DSLAM that employs ATM.
It is noted that while the following description may emphasize the IP multicast over an ATM network, the invention to be described in detail will be equally applicable to other multicasting environment over any DSL access system which may be implemented in other forms of networks, e.g., Ethernet, fiber networks, etc, where virtual circuits or multicast groups can be formed between the host and routing device.
The prior art provides IGMP on a router (IP Server) in an ASAM. The router comprises an IP service module (ISM) and a controller (Network Termination—NT), each being on separate circuit cards. This approach spans two cards. Consequently it is not as efficient as a one-card solution would be. A present Applicant's patent application, Ser. No. 10/878,132 filed on Jun. 8, 2004, describes a solution which uses IGMP termination on the NT for IGMP processing of multicast data streams. This can be called an IGMP on NT architecture. According to the described invention, multicast of the data stream is performed at the ATM level by use of a point-to-multipoint connection, and controlled through IGMP control messages terminating on the NT without usage of the IP Server. This solution is simpler and more efficient than the known systems. It has, however, some performance limitations in that the number of STB (set-top boxes) per NT is limited due to the fact that all the IGMP functions are performed at NT for all the CPEs of the group. Each LT may have many ports, each connected to a CPE (STB) and there are many LTs connected to one NT. As a termination point of IGMP, NT handles all the IGMP control signals for all the connected CPEs. For example, if many end users simultaneously surf video channels, this may overload the NT. Therefore this approach is only appropriate for a very limited video deployment. It is desirable to be able to provide IGMP channel connections in a manner that is scalable.
The invention therefore relates to the problem of providing IGMP services on a DSL access system, such as an DSLAM or ASAM. The invention is applicable equally to the cases where the DSL access system in ATM environment or non ATM environment.